Method of and means for locating alpha light at focal point of lenses



Feb. 12, 1929.

D. J. M CARTHY METHOD OF AND MEANS FOfi LOCATING A LIGHT AT FOCAL POINT OF LENSES Filed Jan. 25. 1926 L: vEmicJR Patented Feb. l2, 192 9.

- UNITED STAlES PATENT OFFICE.

DANIEL J. MCCARTHY, OF ELGIN, ILLINOIS, ASSIGNOR TO CHICAGO RAILWAY SIGNAL & SUPPLY GOMPANY, OF CARPENTERSVILLE, ILLINOIS, A CORPORATION OF ILLI- nors.

METHOD OF AND MEANS FOR LOCATING A LIGHT AT FOCAL POINT OF LENSES.

Application filed January 25, 1926. Serial No. 83,431.

The invention relates to a method of and means for locating a light at the focal point of lenses.

One of the objects of the invention is the provision of an improved method of quickly locating a lamp at the focal point of a lens or combination of lenses and for visually determining, with accuracy, when the lamp occupies the desired position, and means for carrying this new mode of procedure into effect.

Other objects, advantages and benefits of the invention will become apparent to persons skilled in. the art from a considera tion of the following description and the drawings forming a part' of this specification wherein:

Figure 1 is a vertical central section of alens-holding structure with a lamp located at the focal point of the lens combination; Fig. 2 is a fragmentary rear view of Figure 1;

Fig. 3 is a lan view, showing a part in section of a light bending device;

Fig. 4 is a rear end elevation of said device; and

Fig. 5 is an elevation of the beam image receiving surface.

In all of the views the same reference characters indicate similar parts.

When it becomes desirable to reflect light rays or beams from a reflector or to project them through a lens or' lens-combination from a source of light, intense in eflfect, but 'of small contracted dimensions, such asan incandescent lamp with a contracted filament it is very essential for securing the highest efliciency, that the light source be accurately located at the focal point of the reflector or lens.

The most effective known method of accomplishing this result is to adjust the light source or lamp in relation to the lens, and measure the intensity of lightfbeam with a photometer after it passes throu h the lens and after each adjustment is ma e until the most effective osition of the lamp has thus been empirical y found.

By this method or mode of rocedure, the lamp or source of =lightcan elocated at the focal point of the lens or reflectors to yield maximum beam candle power for producing parallel beams, or alternatively diverging beams of any desired spread. This method of procedure will produceaccurate results but it is not available outside of the laboratory.

When the lens-combination is used in signal lights as shown on the drawings, such as railway signals, in which situations they are usually mounted on poles they are, therefore, not accessible for the described photometric determination.

If electric lamps used in such signal devices were indestructible there would be no demand for my lamp focusing invention, because there would be no requirementfor replacement of lamps while the signalling device was in service. Unfortunately, lamps used for the purpose are short lived and the installation of a new lamp in precisely the required position becomes immediately necessary and while the signal device is in service position. Owing to tolerance in commercial reduction of lamps the filament of lamps of the same type and general character vary in position with respect to their attaching means and when placed in the signal devlce the filament may be considerably displaced from the focusing point of the lens. 7

One of the objects of the invention is to provide an improved method and means whereby a new lamp, or a replacement can be accurately located at a focal point of a.

lens or reflector while the apparatus-is in service position and while the operative is in a precarious position on the signal sup.-

portin post or pole.

As s own on the drawings:

The structure is com osed of the "lens 10' and, the'lens,12 and t e color roundel 13. The focal point of this combination is at F. A ray of light, such as 14, striking the lens 10 near its perimeter will be reflected to the angle 15 and when assing thru lens 12 near its perimeter, it w1ll be reflected to the angle 16 and drawn out arallel to the common axis of the, lens com ination. The angles 15 and 16 will bear. a definite relation to each other when the light source is located at F. If the light source be shifted back and forth, the angles 15 and 16 will be changed. Shifting of the focal point F will also cause a change in angle 17.

Angles 17 15 and 16 bear a definite relation to each other and to the lenses.

From this fact it is obvious that "any change in position of the source of light.

from the focal point F will cause a change in the values of these three angles. The operation and results obtained by the device is based upon the foregoing facts.

The focus finding attachment is situated in relation to the lens as to give an indication of any change in the angle of the light rays passing thru lens 10. After passing thru lens 10, light ray 18 is intercepted by the reflector 19 and turned or bent backward as shown at 20. This intercepted ray is caused to impact or strike the transparent 01' translucent plate or disk 21, such as a ground glass plate which is held in definite position with respect to the lens mounting. \Vhen viewed from the rear of the lens mounting the reverted ray of light will appear as a bright spot. When the lamp is at the true focal point of the lens, the spot of light will appear at the center of the disk 21 near the indicated region 22. If the angle ray 18 be changed the position of the spot of light will not appear in the center of the disk. By shifting the light source, the spot of light can be made to appear at 22, the center of the disk 21, at which time the lamp will then be located at the true focal point of the lens. v

The means for segregating and reflecting the beam or ray of light 18, as described, is a removable and replacable housing, consisting of a tubular part 24 and 25. At the? inner junction of these tubes the reflector or mirror 19 is mounted with its reflecting face at a definite angle with respect to the tube 25. The tube 25 has a passage 29 therein thru which the ray 18 is adapted to project. The refracted ray 18 passes thru tube 25, strikes the reflector 19 and is reflected thru tube 24, and impinges on disk 21 as heretofore described.

The tube 24 has a projecting arm 28 integrally formed thereon which carries a lug 30, which enters a hole made in the frame 31 for accurate mounting of the reflector housing.

The frame 31 serves as a support for the lenses 1012 and the roundel 13.

The ring support 31 is held in another ring support 33 which comprises the lamp housmg.

A lamp 35 is removably supported in a socket 36 and the latter is mounted on a vertical stem 37. The stem 37 is vertically adjustible in the clamp 38. The clamp 38 is a part of a horizontal stem 39. The stem 39 is held in a clamp 40 which is a part of the frame 31 and said stem 39 is movable longitudinally in the clamp.

.It is obvious that the lamp 35 may be adjusted and held in any position within the ,on said region of the focusing point of the lens by the arrangement just described.

I am aware that many changes may be made and numerous details of construction may be varied through a wide range without departing from the principles of this invention and I therefore do not purpose limiting the patent granted hereon, otherwise than necessitated by the prior art.

What I claim is:

1. The method of locating a source of light at the focal point of an optical system which includes establishing a light at the focal point by photometric measurements; segregating a ray of light from the focused light near the erimeter thereof and indicating its position; substituting another source of light and adjusting its position in line with said indication to locate said light at said focal point.

2. A focus finding attachment comprising a fixed body; a circular light-receiving and light-projecting body; a source of light near the focal point of the latter body; means for segregating a ray of light near the perimeter of said body and emanating from the focal point of said projector and means for adjusting said light with respect to the aforesaid focal point until the segregated ray therefrom is directed into a predetermined path. I

3. focus .finding attachment comprising a fixed bddy; a lens supported on said body; a lamp supported on said body and adjustable in position with respect to the focal point of said lens; means to intercept a ray of light, after it has passed thru said lens near the perimeter thereof, and bending it rearwardly; a surface to receive said bent ray of light, having an indicating mark thereon and means to adjust the position of said lamp to vary the position of saidbent ray with respect to said mark on said receiving surface.

4. A focus findin attachment comprising a fixed body; a ens supported on said body; a lam movably supported on said body, adjusta le in position with respect to the focal oint of said lens; means su ported ody and removable therefi-om' to intercept a ray of light after it has passed thru said lens near the perimeter thereof; means to accurately position the replaced intercepting means on said body; a lightreceiving surface for said intercepted ray of light; an indicating mark-on said surface and means to adjust the position of the lamp with respect to said mark.

In testimony whereof I have hereunto subscribed my name.

DANIEL J. MCCARTHY. 

